FP1 and rapid shutdown

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FP1 and rapid shutdown

Postby gloomy on Fri May 17, 2019 2:11 pm

I found the article about how to make a Skybox work with rapid shutdown module-level devices from various vendors. But a Skybox is overkill for my application. I am planning a small backup system for power outages with 48v battery and maybe 2 KW of PV. The Skybox seems to want high-voltage PV arrays. How much of that article is applicable to a FlexPower One with FM80 charge controller? It mentions only the FM100.
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Re: FP1 and rapid shutdown

Postby pss on Sat May 18, 2019 9:46 am

I think the first thing you need to figure out is not the voltage of your battery bank, but the amount of load you wish to run off batteries and for how long. A 2000 watt faceplate PV array will maybe average a peak of 1700 watts and say about 5-6 hours per day of output on average for the year depending on your location and temperatures. Using 1500 watts for 5 hours = 7,500 watts of PV per day. Using a 48 volt battery bank means charging the bank at a minimum of 62 volts and it is preferable for your PV output to really be at least 65 volts to the charge controller. So if you install 3 250 watt solar panels in series and then use 3 parallel strings, you will have 2250 watts of output at a high enough voltage to charge a 48 volt battery bank. You could use a Flexmax 60 charge controller for this. Say your battery bank output is at 50 volts and you supplied 7500 watts to the batteries in the day, then 7500/50 = 150 amps of power to charge batteries. If using flooded lead acid batteries or AGM, then you have about 75 amps at 50 volts = 3750 watts available to consume on a regular basis. At 120 volts (AC current to loads from inverter) = 31.25 amps of power. So to get power for a 24 hour day, your average load would be 1.3 amps x 120 volts = 156 watts (actually a little more cause you would have another solar day to keep charging). But you get the gist if it is cloudy. 156 watts will run a laptop and some lights for a day and charge cell phones.

So hopefully this gets you started on thinking about the kind of system you want to install to meet your needs and goals rather than just buying stuff and doing an install and hope technique.
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My RE system: 8330 watts in three strings, Flexmax 60 x 3, Radian 8048A, GSLC load center, Mate 3S, Hub 10.3, FN-DC and 900 Amp, 48V Trojan T105-RE battery bank.

Re: FP1 and rapid shutdown

Postby gloomy on Sat May 18, 2019 11:12 am

The requirement for rapid shutdown is not affected by battery size. But I have done the math on load requirements.

In backup mode (no utility power, such as after a hurricane) the requirement for essential loads is about 3.8 KWH per day. I like to have a 3x margin in case of cloudiness, so figure just around 10 KWH total battery capacity, LiFePO4 batteries. Limited roof space, location of trees, and the fact that most of the available roof faces East, not South, puts an upper bound on how much PV is possible. I figure 8.3 KWH collected daily in in July, but only 4.3 KWH in January. (Figures from pvwatts.org) Hurricanes tend to come in Septermber and October, so array output is going to be in between those limits.

Going with a 48v system voltage reduces max current requirements over, say 24v.

If only the FM100 and the SkyBox have internal support for interfacing module-level shutdown, it looks like the FLEXware Integrated Combiner series may be the way to go, as described in that article, until Outback comes out with new products for smaller systems now that module level shutdowns are becoming a requirement everywhere.
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Re: FP1 and rapid shutdown

Postby pss on Sat May 18, 2019 11:34 am

Thanks for your reply. Using Lithium batteries is completely different. You can safely discharge Lithium batteries about 90% every day. So you are really looking to install 10,000 - 12,000 watts of battery power. This may not be allowed here, but can I ask why you just don't mount your panels, connect them to a Tesla Powerwall 2 or equivalent which will solve your storage and inverter problems and provide the needed power?

Stand alone rapid shutdown solutions can include those like the DC Sunvolt system and the system from Fireraptor. I believe they can be installed on any Outback System.
pss
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My RE system: 8330 watts in three strings, Flexmax 60 x 3, Radian 8048A, GSLC load center, Mate 3S, Hub 10.3, FN-DC and 900 Amp, 48V Trojan T105-RE battery bank.

Re: FP1 and rapid shutdown

Postby gloomy on Sat May 18, 2019 11:50 am

Batteries are measured in Watt-Hours, not Watts. :)

Tesla Powerwalls are high-voltage devices with integrated inverters, so that changes everything over to being AC-coupled and a separate PV inverter. Plus you still nead the bypass and grid-disconnect functionality somewhere. I prefer a more integrated solution with most parts from a single supplier, and preferably in a single box. The Outback FP1 systems provide that. Powerwalls also have high lead times.

Because of my limited roof space, there is no way I can power more of my house beyond the essential stuff, and half of that is the refrigerator. So there is no need to look at systems aimed at whole-house solutions.
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Re: FP1 and rapid shutdown

Postby pss on Sat May 18, 2019 12:31 pm

Batteries will have a "capacity" rating. Generally this is expressed as the amount of power that can be used in a measured period of time. Commonly a 4 hour, 20 hour and 100 hour capacity may be available on the label or spec sheet. Power is expressed as watts. Watts are Amps x Volts. Solar voltage from the panels is DC current (Amps) sent to the batteries from the charge controller to bring the battery to full capacity (fully charged). Batteries store power (ie. wattage) which is released in the form of current (the flow of power, Amps) at a specific voltage over a period of time. Total battery capacity (power or wattage) is reduced if the discharge amperage rate is higher rather than lower. DC power stored in a battery is converted to AC power by the inverter. AC watts and DC watts are still watts. Watts are power. What you choose to do with those watts of power stored in the battery are entirely up to you. And how fast you choose to consume your watts of power is also entirely up to you. So battery capacity (power) is expressed as watts. But since batteries are used for different purposes (starting a car or powering a home) a more convenient and useful term is Amp Hours (the discharge rate in amps for a specific voltage over a fixed period of time). Automobile starting batteries are required to produce a high amperage for a short period of time (CCA or cold cranking amperage) to turn over a gasoline or diesel motor. Batteries used in electric backup situations are usually built and sized to supply a known load range for an expected period of time. That is where knowing battery capacity in hours is more useful than total wattage (power) stored by a battery. But, if your battery is say 24,000 watt capacity and your PV generates 8,000 watts per day, you will need three good solar days to charge your battery to capacity if discharged. So, in my preceding post, I somehow insulted you by referencing the term "watts of battery power". I used it to mean the total wattage of the battery bank. Not the capacity of the bank to deliver power over time (what you call a watt-hour). My battery capacities are commonly compared at the 20 hour rate of available amperage. So for a six volt battery with a 20 hour capacity of 225 amp hours, this means that the discharge rate is 11.25 amps per hour at 6 volts or 67.5 watts. But, connected to my inverter and using the power at 120 volts (with a fantasy of 100% efficiency) means it only supplies to me 0.5625 amps of power. If I connect them to become 48 volts, then I get 540 watts of power, then I can draw 4.5 amps at 120 volts for 20 hours. Of course, these are not lithium batteries, so I cannot really discharge them down by 90% or I would ruin them. So apologize for using the term "measured" when referring to batteries. Thanks for pointing that out.
pss
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My RE system: 8330 watts in three strings, Flexmax 60 x 3, Radian 8048A, GSLC load center, Mate 3S, Hub 10.3, FN-DC and 900 Amp, 48V Trojan T105-RE battery bank.

Re: FP1 and rapid shutdown

Postby gloomy on Sat May 18, 2019 1:10 pm

Avearge draw over the day is only 155W. But if the refrigerator compressor decided to run just as I switch on the microwave to make tea. it might be ten times that. But running the microwave is likely to happen when the Sun is shining, so not affect the battery that much. In the hurricane scenario, having been through a few of them, the clouds clear up considerably within 24 hours after peak wind. That is why the 3x factor in battery size, to get through that period. One time it took the utility 3.5 days to get service restored.

Max continuous discharge current for the batteries I am considering is 34A, and with 3 of those in parallel I am well away from the nasty part of the discharge curve. The rated capacity at C/2 is 3.5 KWH per battery. (SimpliPhi LiFePO4) I try to stay away from the speced limits on everything.
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Re: FP1 and rapid shutdown

Postby pss on Sat May 18, 2019 2:01 pm

We used to live in Palm Beach County. We were hurricaned out of home too. We got power back in 24 hours cause of our utility pole connection, neighbors were without power for 8 days. But you are right about it clearing up very quickly. My only concern would be that there could be wind damage to panels or wiring or structure housing the inverter as well as potential for flooding and maybe grounding problems. Not to mention debris causing damage to the system. A lot of new homes in Palm Beach County that are custom built have a shielded protected portion of the roof for panels. But if system survives the storm well then you are good to go. I never really looked into it, but maybe you can fashion some type of hurricane shutter to install over the surface of the panels during the storm for protection. Maybe even like the old crank style shutters or some other roll away type. By the way, my Radian easily can run a 3K load and still provide enough surge power to start my 5HP table saw motor which Delta says can surge to 32,000 watts to start up. But there is a big starting capacitor and running capacitor on the motor to help.
pss
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Posts: 232
Joined: Mon Jul 24, 2017 8:40 am
My RE system: 8330 watts in three strings, Flexmax 60 x 3, Radian 8048A, GSLC load center, Mate 3S, Hub 10.3, FN-DC and 900 Amp, 48V Trojan T105-RE battery bank.


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